As is known in the art, one technique used to cool electrical components in cabinets is with fans. The amount of airflow (and thus the cooling) through the cabinet is controlled by adjusting the speed of the fans. The individual fan speed is typically adjusted by varying the duty-cycle of a Pulse-Width-Modulated (PWM) control signal that is the control input to the fan and the actual fan speed is monitored by a tachometer producing a feedback control signal.
As is also known in the art, in some cabinets, electrical components are electrically interconnected through a backplane (sometimes also referred to as a midplane). One such an arrangement is used in data storage systems wherein disk drives are plugged into one side of the backplane and storage processors used to control data to and from the disk drives are plugged into the other side of the backplane. In such arrangement, a plurality of fan units is mounted to the rear, exposed region of the storage processor. With such an arrangement, when one of the fan units is detected as having failed, the technician can easily replace the failed one of the fan units.
In some application, however, the fan units must be mounted towards the rear, unexposed, region of the storage processor (i.e., the region within the cabinet nearer the backplane) thereby requiring that the storage processor be shutdown in order to remove the failed one of the fan units. This is obviously an undesirable situation.